Composite pigments and process of making the same



iPatented Aug. 2 7, 1940 2,213,168 COMPOSITE I IGMENTS AND PROCESS OFMAKING THE SAME Reginald Hill Monk and Archibald Stewart Ross,

Montreal, Quebec, Canada, assignors to American Zinc, Lead & SmeltingCompany, St. Louis, Mo., a corporation of Maine No Drawing. ApplicationJuly 30, 1938, Serial No. 222,299

5 Claims. (Cl. 134-58) This invention relates to composite pigments oflow reactivity and high-whitening strength and a process for producingsuch pigments.

For the purpose of brevity and clearness of 5 description the symbolsMO, MO .and R02 are used herein and are to be understood as meaning--- ao MO=' Ihe oxides of magnesium, zinc, cobalt,

no nickel, manganese, iron, chromium and/or vanadium, or any combinationthereof;

M'O=The oxides of calcium, strontium, barium and/or lead, or anycombinationthere- 16 Y of R02 =The oxides of titanium, zirconium,thorium and/or tin or any combination thereof.

Compound pigments of the type ZMQROn where MO is the oxide of a divalentmetal such as magnesium or zinc, and R02 is the oxide of titanium, areknown in the art. (U. S. Patent No. 2,085,165 and German Patent No.648,518),

Compound pigments of the type M'O.RO2, when Q5 MO is the oxide of adivalent metal, such as calcium or lead, and R02 is the oxide oftitanium, are also known in the art. (U. S. Patent No. 1,760,513 and1,856,351).

Experience and careful test have demonstrated that compounds of the2MO.ROz type are of low pigmentary value; and compounds of the M'O.RO2type are unsatisfactory, for while giving a high degree of opacity theyare usually of a poor color in themselves or are easily 3 discolored bytraces of impurities, and when zinc oxide or white lead are addedthereto in quantities necessary to give a correctly proportionedformula, the composite mixture is highly reactive with vehicles such aslinseed oil or gum varnishes or with'cellulose varnishes in which gumbases are used.

The fundamental object of the present inven-= ,tion is to provide mixedor composite pigments containing the components existing in the com- Q5pounds of the ZMOROz type but combined in newv proportions with theMIG-R02 type in which compound pigments the reactivity of the reactivecompoi nds is greatly reduced without sacrifice of whitening strength.-A further object is to 5% provide an operative method whereby suchcomposite pigments may be produced.

With this end in view, a compound of 2MO.RO2 (where MO is the oxide ofmagnesium, zinc, cobalt, nickel, manganese, iron, chromium and/or 55vanadium or any combination thereof which combines with an oxide of theR02 type to form a compound 2MO.RO2 asthe normal form) is mixed inequimolar proportions with a compound of 2MO.RO2 (where (MO- isthe'oxide of calcium, strontium, barium and/or lead or 5 any combinationthereof) combining with oxides of the R02 type to form a compound M'OBOzas its normal form). The components 2M'O and R02 at calcinationtemperatures form the compound vMO.RO 2 together with free oxide MO, but10 we have discovered that in the presence of the normal compound of theformula 2M0.RO2, the

total'mixture when calcinedv possesses to' a remarkable degree the lowreactivity of a compound of the type 2MO.R02 and the high opacity'of thecompound M,O.R0z. These characteristics suggest the formation of apseudomorphic compound of theformula (2MO.RO2).(2M'O.R02), in which theoxide M'O behaves as if it. were an oxide ofthe type M0. Within thelimits of the formula of the equimolar compound between the normal2MO.RO2 and the pseudomorphic 2M'O.R.Oz, mixtures of any of the oxidesof the MO, MO or R0 types may be substituted for any single oxide. maybe mixtures of a number of oxides falling within the respective groups.For instance, 2MO.RO2 may represent in its simplest form 2ZnO.TiO2 butit also might imply such a mixture aswould be represented by the formulaor more generally, 2(ZnO,MgO) .(TiOz,ZrO2). The essential feature of theinvention however is the combination of compounds of this type withequimolar proportions of what is really a hypothetical compoundrepresented by the other half of the formula, namely, 2M'O.RO2. Inthishalf of the formula, the simplest form of the compound may berepresented by the formula 2CaO.TiO2. This, however, may be againexpanded into a mixture of oxides such as would be represented by theformula 2(0.5CaO+0.5PbO) 0'.'1'rioz+0.3sno2) or more generally again a(CaOJPbO) .(TiO2,SnO2) 5 Thus both sides of the formula calciumchloride.

desired synthesis of be Written pigmentary properties, may

.used and which are to be understood to be taken in summation as equalto one mol of the respective type of oxide. The oxides of magnesium,zinc, cobalt, nickel, manganese, iron, chromium and vanadium are oxideswhich form compounds of the 2MO.RO2 type; and the oxides of calcium,strontium, barium, and lead are oxides which form compounds of theMO.RO2 type, and can form pseudomorphs of the 2M'O.RO2 type. But it isto be understood that any other oxides or salts decomposable into theiroxide componentswhich form compounds of the respective types are withinthe scope of the invention. Moreover, in the case of those compositescontaining the oxides of the normally polyvalent metals Mn, Fe, Cr, andV, the correct oxidation-reduction potential in the calcining atmospheremay be obtained by calcining in the presence of a reducing gas or bysubstituting for part of the oxides the respective metals and calciningin an inert atmosphere. And it is further to be understood that byoxides of the R02 type ismeant the oxides of titanium, zirconium,thorium and tin. The oxides may be prepared in the wet way or the myway, and a mixture of oxides may be employed instead of a single oxide,provided that the total mols of the mixture of oxides equals the numberof mols of the single oxide for which they are substituted, and it is tobe understood that when mention is herein made of an oxide, that termincludes, and is intended to include equivalent mixture of such oxides.

In practicing the invention the material should be prepared in a highstate of dispersion to secure the maximum degree of combination. C0-

precipitation'from solution is an ideal-method I when feasible from aneconomical point of view.

Or solid reagents may be ground together in the proper molar proportionsin cases where a somewhat greater degree of reactivity is permissible.Furthermore a mixture of solid and liquid reagents may be employed insome cases. For example, zinc oxide prepared by the usual process ofoxidizing zinc sulfide may be combined with freshly precipitated T102and then calcium carbonate may be intimately dispersed among these twosolids by precipitation from a solution of Moreover, solid reagents maybe used when these are decomposable by heat or in reactions with othercomponents of the mixture during calcination.

The following are specific examples of the practice of the process:

Example 1.Two mols of calcium chloride are dissolved in water to give a'solution containing ten percent by weight of calcium chloride. Thissolution is mixedwith two mols of precipitated TiOz which has beendispersed by the addition of approximately ten percent by weight on thedry TiOz content of barium chloride dihydrate. The mixed suspension thusprepared is then added under vigorous agitation to two mols ofcommercial .zinc oxide previously prepared in aqueous suspensioncontaining approximately twenty-five percent by weight of dry zincoxide. To the mixture containing the TiOz, Z110 and CaClz, two mols ofsodium carbonate in aqueous solution containing ten percent anhydrousNazCOs are added under vigorous agitation and the resultant intimatemixture of solids consisting of ZnO, T102, CaCO; (together with a smallamount of Basoi) is filtered off, thoroughly washed and calcined toapproximately 900 0., whereby the calcium carbonate is decomposed intoCaO and CO2 and reaction between the ZnO, T102 and CaO takes place togive the compound (2ZnO.'IiOz).(2CaO.TiOz) substantially as described.

Example 2.The above compound may be prepared from commercial lime byremoving its impurities in the following manner:

Sufiicient commercial lime to give 2 mols of calcium chloride is treatedwith a 10% solution of ammonium chloride. The exact amount of limerequired is determined by experiment since the percentage oi availablelime soluble in amm-onium chloride varies with the thermal treatment towhich the calcium carbonate has been' subjected in the burning process,as well as the amount of insoluble impurities, particularly magnesia andsilica. The suspension of lime in reaclon wth ammonum chloride attemperatures from to C. gives a solution of calcium chloride andammonia. In view of the volatility of the ammonia, the reaction ispreferably carried out in a closed vessel fitted with a refluxcondenser. The solution is then cooled to approximately 60 or 70 C. andto the reaction vessel is added, under agitation, 2 mols of ZnO mixed toa thick paste with water. Carbon dioxide is then passed into the mix andin the presence of the ammonia the calcium chloride is rapidly convertedto calcium carbonate, the reaction being completed in 15 to 30 minutesunder a gauge pressure of 15 lbs. CO2. At the conclusion of the reactionthe suspension is filtered off and the filter cake is thoroughly mixedwith 2 mols of precipitated T102. The filtered liquor containingammonium chloride is made up to its original strength as by suitableadditions of dry ammonium chloride and is returned to the reactionvessel.

The mixture of the filter cake with TiOz is filtered oh and calcined atapproximately 900 C. to give the same product as in Example 1.

Example 3.A solution of lead acetate of approximately 1.04 specificgravity is allowed to act upon granulated lead in the presence of air atapproximately 30 to 35 C.. The basic lead acetate solution thus formedis precipitated by C02 and allowed to settle. After filtering off thebasic lead carbonate, Pb(OI-I)2. 2PbCOz, the lead acetate solution isreturned to the reaction chamber to react with more lead.

mol of the precipitated basic lead carbonate is condensed in an edgerunner for 20 to 30 minutes with 2 mols of commercial zinc oxide and 2mols of precipitated TiOz. The mixture is then calcined to about 800 to900 C. to give the compound (2ZnO.TiOz).(2PbO.TiO2).

It will be found that in the use of the composite pigment produced bythe process described, the reactivity of the reactive components isgreatly reduced While the whitening strength remains unimpaired.

What is claimed is: l v

1. A composite V pigment consisting of (2 MO.'IiOa).-(2M'O'.Ti0a), whereMO is at least one of the oxides of the group ZnO, MgO, C00, N10, MnO,FeO,' 010, V0 and M'O is at least one'of the oxides of the group CaO,SrO', BaO, and Rho. p 1

2. A composite pigment consisting of (2ZnO.TiO2).(2M'O.T102) where NYCis at least bonate of sodium, filtering ofi the mixed commagnesium,"chromium and vanadium which-combine with posite precipitate andcalcining it at atemperature of approximately 900 C 4. A compositepigment (2 ZnO.TiO2)'.(2CaO.TiOz) 5, The process which consists inmixing a compound of the 2MO.TiO2 type, where MO is one or.more of theoxides of the elements zinc, cobalt, nickel, manganese, iron,

consisting 1 of TiO; to form a compound 2MO.'-Ii02 as the normal form,withequimolar proportions of a compound of the pseudomorphic 2M'O.Ti0type, where M'O is one or more of the oxides of the elements, calcium,strontium, barium and load which combine with TiOgz to form a compoundM'O.Ti02 asits normal form, and-then calcining the mixture,

' REGINALDHILL' MONK.

ARCHIBALD STEWART ROSS.

